Discharge tube with beam forming grids



Oct. 26, 1937. H. ROTHE El AL DISCHARGE TUBE WITH BEAM FORMING GRIDS Filed 001;. 28, 1956 INVENTORS HORST ROTHE WERNER KLEEN AND g bYALTER GRAFFUNDER ATTORNEY Patented Oct. 26, 1937 UNITED ST rs DISCHARGE TUBE l/VITH BEAM FORMING GRIDS Germany Application October 28, 1936, Serial No. 107,942 In Germany November 13, 1935 5 Claims.

The invention relates to electron discharge devices, especially the geometry development of grid electrodes for discharge tubes, and in particular to tubes for generation, amplification and rectification of alternating potentials.

The prior art has used many grid shapes, all having the common characteristic feature that their cross-section at right angles to the cathode or to the axis of the electrode system is either straight or is curved to be concave towards the cathode surface. As examples, reference may be made to plane, circular-cylindrical, oval-cylindrical, conical, globular, or prismatic grids. An investigation of the electron flow in a tube equipped with this type of grid shows that these grids exert a stray scattering action on the electron stream passing through them and, for instance, widen out an electron ray passing through them to a diverging bundle, or increase the divergence of a beam which arrives within a certain spatial angle. Now, it is not only important in cathode ray tubes for oscillographs and television operation, but is also useful for many purposes in amplifiers to bundle the electrons, and in particular, to cause them to follow parallel or converging paths in a part of discharge space. In this way it is possible, for instance, to protect the support rods of grids impressed with positive potential against electronic bombardment, which causes an undesirably high current pick-up due to the relatively large surface of the grid rods by guiding the electrons around these rods. The current load of suitably constructed screen or space-charge electrodes can accordingly be decreased or even entirely suppressed. Moreover, control grids may be modulated over a positive grid potential range without noticeable current pick-up. The use of concentrated electron streams or beams is further known in the art in connection with various types of electron multipliers and finally arrangements for the control of high-speed electrons have been proposed by the prior art which utilize the change in direction of an electron beam; that is, of a concentrated discharge. The concentration of electron streams is known from the prior art of cathode-ray oscillographs and Braun tubes; for this purpose use is made of magnetic or electric concentration means, hollow cathodes, or diaphragms. These means are partly cumbersome and not generally known in the art of tube amplifying, since they do not adapt themselves readily for use with the usual cylindrical or box-like electrode systems with filamentary, cylindrical, or plane cathodes.

The object of the invention is to provide beam focusing means suitable for use in amplifying tubes which are in general of conventional construction, and in accordance with the invention, at least one of the grid electrodes that follow the cathode in the direction of discharge and are adapted to let the current pass is developed in such manner that it is convexly curved towards the emission surface. In line cathodes this is understood to mean that the electrode in question has a convex curvature to the cathode surface in a cross-section at right angle to the axis of the cathode. The grid surface may be composed of several surfaces set at an angle to each other, and constituting the sides of a prism, and the grid may in this way supply a number of electron. beams corresponding to the number of surfaces.

The invention will best be understood by reference to the accompanying drawing, in which Figure l is a cross-section of one form of embodiment of the invention, and Figure 2 is a crosssection of another form utilizing the conjoint action of two grids made in accordance with the invention.

In the embodiment of the invention shown in Figure l a linear cathode k is surrounded by a grid electrode consisting of four grid rods 3, of wire or of insulation, on which is wound the grid conductors or grid wire g of such form that the grid wires lie in a cylindrical surface convexly curved towards the surface of the cathode is. It is in itself of no importance whether the grid consists of a wire wound helically on the supports, or of a mesh-like sheet, or of metallic cloth, or again of wires or strips running parallel to the supports and connected to rings at their ends. In each case the desired convex form may be easily obtained by pressing or the like. The grid as illustrated consisting of four sections, supplies four individual electron beams, each passing between two adjacent grid supports and whose width is equal to the length of electrode system. The action of a grid of this type may therefore be compared with that of a cylindrical lens. Another electrode, for example a grid-like electrode having rod conductors 1) parallel to the cathode, may be mounted between the anode a and the grid with its conductors between the beams from the grid, so that it will collect substantially no current from the beams even when at a positive potential.

In the embodiment shown in Figure 2 the cathode k is surrounded by two coaxial grids g1 and g2 which in structure and form corresponds to the grid of Figure l. The action of grids of such form may be determined by calculation. In the surface of the first grid an effective potential 11,1 exists, and in the surface of the second grid an effective potential uz. Assuming further that the two grids have the same radius of curvature r, calculation shows that the grid arrangement as shown acts as a converging electron lens with the focal length Thus a beam path course of the discharge current is obtained which has been confirmed experimentally by tests with probe electrodes. The charactertistic paths e of single electrons have been plotted in Figure 2. As the formula shows, the shape of the electron path depends not only on the curvature of the grids, but also on their potential ratio, opening thus new possibilities for the control of the electron stream by shifting the focal point, and for the adjustment of the quiescent position of the electron beam and for correction of inaccuracies of electrodes. Slat anodes or pick-up electrodesa may be mounted in the paths of the electron beams, at or near the focal points, if narrow anodes are desired.

The electron concentration obtained in the described way may be utilized in any desirable manner. It may, for instance, be used for the purpose mentioned previously of relieving the current load of positive electrodes or of limiting the spread of the pick-up electrodes to the surface hit by the electrons or again the electron ray may be subjected to control of direction and may be made to impinge more or less completely and alternatingly on different pick-up electrodes.

In the embodiments the action of a cylindrical lens was sought to be obtained with its axis parallel to the linear cathode. It is obvious that spherical lens action may also be obtained by assuming a flat or point-like electron source and imparting to one or several grids the form of a portion of the surface of a globe curved convexly towards the cathode in two directions at right angles to each other.

We claim:

1. An electron discharge device comprising a cylindrical cathode, an anode, and two tubular grid electrodes of different diameters mounted coaxial with said cathode, each of said grid electrodes having spaced grid conductors curved to lie in a semi-cylindrical surface convex to said cathode, said semi-cylindrical surfaces having the same radius of curvature and being mounted to be traversed in succession by the discharge from said cathode to said anode.

2. An electron discharge device comprising a linear cathode, an anode, and a grid electrode interposed between said cathode and said anode and comprising space grid conductors curved to lie in semi-cylindrical surfaces convex toward the cathode and intersecting at the corners of a prism.

3. An electron discharge device comprising a linear cathode, a prismatic grid electrode having spaced grid conductors curved to lie in a curved surface convex to said cathode in a cross-section at right angles to said cathode, an auxiliary gridlike electrodes comprising spaced rod conductors parallel to said cathode and in radial alignment with the corners of said prismatic grid electrode, and an anode exposed to said cathode through the gap between said rod conductors.

4. An electron discharge device comprising a linear cathode, a tubular grid electrode comprising several grid rods parallel to said cathode and forming corners of a prism, and spaced grid conductors extending transversely of said grid rods and curved to lie in a semi-cylindrical surface convex to said cathode, an auxiliary electrode of spaced rod conductors parallel to and aligned with said grid rods radially of said cathode, and an anode exposed to said cathode through said auxiliary electrode.

5. An electron discharge device comprising a cylindrical cathode, a slat anode parallel to said cathode, a grid electrode comprising a pair of grid rods parallel to said cathode and on opposite sides of a straight line between said anode and said cathode and spaced grid conductors extending between said grid rods and curved to lie in a semi-cylindrical surface convex to said cathode, and an auxiliary electrode comprising rod conductors parallel to and aligned with said grid rods radially of said cathode to form with said grid electrode an electron lens to focus at or near said slot anode an electron discharge from said cathode through said grid to said anode.

HORST ROTHE. WERNER KLEEN. WALTER GRAFFUNDER. 

